Unidirectional correction systems for a time displaying device are known. For example, patent document EP-B-0 173 230 (US-A-4 634 287) describes a universal timepiece including a date ring and a disc which are stepped every twenty-four hours. In accordance with whether the time setting stem is rotated in one sense or in the other, the indications given by the ring or respectively the indications given by the disc are corrected. The mechanism employed is a shifting intermediate wheel with teeth and a three-toothed pinion. If the stem is operated in one sense, the intermediate wheel is placed in a first position in which the teeth are in mesh with the disc. If the stem is operated in the opposite sense, the intermediate wheel is placed in a second position in which the pinion is in mesh with the ring. In such a construction, several wheel sets are interposed between the control stem and the time indicator which is to be corrected, this leading to a relatively complicated and difficult construction.
Patent document CH-A 607 556 has as its purpose to eliminate such wheel sets and to correct a date ring directly from a pinion sliding on the time setting stem. For this, the sliding pinion exhibits an annular groove in which is frictionally assembled a spring wire surrounding the groove over slightly more than three quarters of its periphery. A free end of the spring wire projects radially beyond the periphery of the sliding pinion and directly serves as driving finger in order to advance or draw back the date ring by turning the stem respectively in one or the other sense. Interesting though it may be, this construction does not lead to the solution proposed by the present invention, namely a unidirectional correction arrangement since the spring wire of the cited document acts on the date ring in both correction senses. This is a bidirectional arrangement.
Patent document CH-A-290 100 describes a unidirectional control system for winding up an alarm device. On the winding stem are mounted, one following the other, two sockets of the same diameter on which a helical spring is wound. One of the sockets is fixed to the stem while the other is free to rotate on such stem. The free socket is fixed to a toothed wheel, itself fixed to a barrel spring. When the stem is driven in rotation in one sense, the helical spring is tightened around both sockets in order to couple them together and thus wind the barrel spring. When the stem is driven in rotation in the other sense, the helical spring is loosened and the free socket is not driven. There, however, it concerns a coupling system in which the helical spring may act only if it encloses two elements (two sockets) placed side by side, which has nothing in common with the present invention in which the helical spring encloses only a single element (a sliding pinion) and where such spring exhibits a raised end which drives a second element (a date disc).
The interest in a unidirectional correction system may be seen in the economy of the means employed when it concerns the correction of an entire series of time indicators as is evoked in the first document cited hereinabove: when the stem is rotated in one sense, the data is corrected for one indicator and when the stem is rotated in the other sense, the data is corrected for another indicator. Another interest may be seen quite plainly in the simplification which it brings to the driving mechanism for the indicator in question. It is known, for example, that the driving mechanism may give rise to problems of good operation if the time indicator can be manually corrected in both senses.